Various implantable medical devices have been clinically implanted or proposed for therapeutically treating or monitoring one or more physiological conditions of a patient. Such devices may be adapted to monitor or treat conditions or functions relating to heart, muscle, nerve, brain, stomach, endocrine organs or other organs and their related functions. Advances in design and manufacture of miniaturized electronic and sensing devices have enabled development of implantable devices capable of therapeutic as well as diagnostic functions such as pacemakers, cardioverters, defibrillators, biochemical sensors, and pressure sensors, among others. Such devices may be associated with leads to position electrodes or sensors at a desired location or may be leadless, with the ability to wirelessly transmit data either to another device implanted in the patient or to another device located externally of the patient, or both.
Although implantation of some devices requires a surgical procedure (e.g., pacemakers, defibrillators, etc.) other devices may be small enough to be delivered and placed at an intended implant location in a relatively noninvasive manner, such as by a percutaneous delivery catheter. By way of illustrative example, implantable miniature sensors have been proposed and used in blood vessels to measure directly the diastolic, systolic and mean blood pressures, as well as body temperature and cardiac output. As one example, patients with chronic cardiovascular conditions, particularly patients suffering from chronic heart failure, may benefit from the use of implantable sensors adapted to monitor blood pressures. As another example, subcutaneously implantable monitors have been proposed and used to monitor heart rate and rhythm, as well as other physiological parameters, such as patient posture and activity level. Such direct in vivo measurement of physiological parameters may provide significant information to clinicians to facilitate diagnostic and therapeutic decisions. If linked electronically to another implanted therapeutic device (e.g., a pacemaker), the data can be used to facilitate control of that device. Such devices also, or alternatively, may be wirelessly linked to an external receiver. In addition, because these devices are implanted within a patient, battery life, the size of a battery or other on-board power sources for the device, and the ability or the difficulties associated with recharging the battery or other on-board power sources is an important consideration in determining what functions and features may be provided and/or may be available in any given system involving implanted medical devices.